試圖調用虛擬方法'android.support.v7.app.AlertDialog android.support.v7.app.AlertDialog $ Builder.create（）'null對象引用

Question

我每次構建我的應用程序時遇到了錯誤Attempt to invoke virtual method 'android.support.v7.app.AlertDialog android.support.v7.app.AlertDialog$Builder.create()' on a null object reference

這裏是我的錯誤

07-26 15:04:32.587 18897-18915/com.example.study E/AndroidRuntime: FATAL EXCEPTION: Thread-385 
Process: com.example.study, PID: 18897 
java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v7.app.AlertDialog android.support.v7.app.AlertDialog$Builder.create()' on a null object reference 
    at com.example.study.Splash.checking(Splash.java:66) 
    at com.example.study.Splash$2.run(Splash.java:51) 

事情發生在我的濺活動的代碼，這是我的代碼

package com.example.study; 

import android.content.DialogInterface; 
import android.os.Bundle; 
import android.support.v7.app.AlertDialog; 
import android.support.v7.app.AppCompatActivity; 

import com.example.study.helper.SessionManager; 
import com.example.study.util.ConnectionDetector; 

public class Splash extends AppCompatActivity { 

    private ConnectionDetector cd; 
    Boolean isInternetPresent = false; 
    protected SessionManager session; 

    private AlertDialog.Builder builder; 


    @Override 
    protected void onCreate (Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_splash); 


     AlertDialog.Builder builder = new AlertDialog.Builder(Splash.this); 

     session = new SessionManager(getApplicationContext()); 
     cd = new ConnectionDetector(getApplicationContext()); 

     builder.setTitle("No Connection"); 
     builder.setMessage("Check Your Internet Connection."); 
     builder.setIcon(R.drawable.fail); 
     builder.setPositiveButton("OK", new 
DialogInterface.OnClickListener() { 

      @Override 
      public void onClick(DialogInterface dialog, int id) { 

        /* TODO Auto-generated method stub */ 
       dialog.dismiss(); 
      } 
     }); 

     Thread timer = new Thread(){ 
      public void run(){ 
       try { 
        sleep(2000); 
       } catch (Exception e) { 
        e.printStackTrace(); 
       } finally { 
        checking(); 
       } 
      } 
     }; 
     timer.start(); 
    } 

    public void checking() { 

     isInternetPresent = cd.isConnectingToInternet(); 

     if(isInternetPresent) { 
      session.checkLogin(); 
      finish(); 
     } else { 
      builder.create().show(); 
      finish(); 
     } 
    } 
} 

不知道該怎麼辦...請幫助解決這個問題，

Answer 1

我認爲它在您的checking()方法失敗。您已聲明一個名爲builder的全局變量，然後在onCreate()內聲明另一個變量。在你的checking()方法中，它指的是你沒有初始化的全局變量，只聲明。

可能的解決方法，編輯這個：

AlertDialog.Builder builder = new AlertDialog.Builder(Splash.this); 

到

builder = new AlertDialog.Builder(Splash.this);